Add license information to files for matrix-conduwuit

This commit adds copyright attributions in SPDX to the files for matrix-conduwuit, following REUSE's specification.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

roles/custom/matrix-conduwuit/defaults/main.yml

@@ -1,3 +1,8 @@
+# SPDX-FileCopyrightText: 2025 MDAD project contributors
+# SPDX-FileCopyrightText: 2025 Slavi Pantaleev
+#
+# SPDX-License-Identifier: AGPL-3.0-or-later
+
 ---
 # conduwuit is a very cool, featureful fork of conduit (https://gitlab.com/famedly/conduit).
 # Project source code URL: https://github.com/girlbossceo/conduwuit